The present invention is related to a pneumatic tool, and more particularly to a pneumatic cylinder of a pneumatic tool. The pneumatic cylinder is capable of avoiding loss of lubricant of the bearings so as to prolong the using life of the pneumatic cylinder.
FIG. 1 shows a conventional pneumatic cylinder 10 having a cylinder body 11. Referring to FIG. 2, the cylinder body 11 has an inlet 13 and at least one outlet 14, whereby the high pressure air can flow into the cylinder chamber 12 of the cylinder body and then flow out of the cylinder body. A rotor 15 is accommodated in the cylinder chamber 12 and fixedly connected with a rotary shaft 16. Two end caps 17 cover two ends of the cylinder body 11. The rotary shaft 16 extends out of the cylinder body 11 through the through holes 171 of the end caps 17. Two bearings 18 are located in the cavities 172 of the end caps 17 and fitted on two ends of the rotary shaft 16. When the rotary shaft rotates, the bearings 18 serve to support the rotary shaft.
The pneumatic cylinder 10 is mounted in a receiving space 19 of the pneumatic tool. After the high pressure air flows into the receiving space 19, the high pressure air will flow into the cylinder chamber 12 of the cylinder body 11 from the inlet 13 and then flow out from the outlet 14. When the high pressure air flows in the cylinder body, the high pressure air drives the rotor 15 and the rotary shaft 16 to rotate and operate.
The pneumatic tool utilizes high pressure air as power source so that the pressure of the air is quite high. In addition, a great amount of high pressure air is input into the cylinder chamber 12 and then exhausted from the outlet. The air cannot flow out from the outlet 14 in time will find other way to escape. Since the rotor and the rotary shaft rotate at high speed, a small gap exists between the wall of the through hole 171 of the end cap 17 and the rotary shaft 16 to avoid high heat caused by high speed friction. Accordingly, a little high pressure air in the cylinder chamber will quickly escape through the gap. Although the escaping air is little in comparison with the input air, such escaping air still has a considerable impact due to high pressure and high flowing speed. After flowing out from the through hole 171 of the end cap, the high pressure air flows through the gap between the bearing 18 and the cavity 172 into the bearing. After flowing into the bearing, the high speed air will blow out and dissipate the lubricant painted between the inner and outer rings 181, 182 of the bearing. After a period of time, the lubricant in the bearing will be totally lost.
In the case that the bearing lacks the lubricant, high heat will be generated in operation. Moreover, the components will directly abrade each other for a long time. This will lead to deformation and clog of the components. Practically, it is found that the high speed pneumatic tool such as pneumatic grinder often malfunctions after used for several months. The fault is caused by the failure of the bearings. As a result, a user needs to frequently service the pneumatic tool or purchase a new one.
Furthermore, after the lubricant is blown away from the bearing, the lubricant will splash over the wall face of the receiving space 19 of the pneumatic tool. Therefore, the receiving space will be contaminated by a great amount of dirt and dust. This often leads to faults of the components of the pneumatic tool.